Pressure control system for aircraft cabins



Feb. 16, 1943. N- C PME Re. 22,272

PRESSURE CONTROL SYSTEM FOR AIRCRAFT CABINS Original Filed July 19, 193'? 3 Sheets-Sheet l Smaentot Nathan C. Price QZ/Z4 Gttorneg Feb. 16, 1943. A N Q PR|CE Re. 22,272

PRESSURE CONTROL SYSTEM vFOR AIRCRAFT CABINS Original Filed July 19, 1937 3 Sheets-Sheet I5 |2345 67 BSIOHIZISHIlIT Thousands of Feet Elevaion Naham C. Price Gum-neg Ressued Feb. 16,* 1943 PRESSURE GONTML SYSTEM FOB AIRCRAFT C ABINS Nathan c. rri. nouywwa, cam.. salgan, by

mesne assignments, to Boeing Aircraft Company, Seattle, Wash., acorporatlon oi Wash- Original No. 2,208,554, dated July 16, 1940, Serial No. 154,438, July 19, 1937. Application for reissue November 12, 1940, Serial No. 865,396

89 Claims.

In order to promote the comfort of passengers in airplanes designed to ily at high altitudes, and indeed to avoid harmful physiological efi'ects upon the passengers and crew, due to low pressure at high altitudes, it is necessary to supercharge the cabins of high altitude aircraft. However. there is a point beyond which supercharging cannot be carried practically, for the reason that if an attempt is made to maintain within the cabin an absolute pressure level (for instance if it is attempted to maintain sea level pressures or pressures not lower than some given pressure a1- titude) at appreciably higher altitudes, there are produced bursting stresses to contain which necessitates very greatly strengthening the cabin and reinforcing it. The -added weight makes the aircraft, because of reduction of pay load, eco` nomically impracticable. It becomes necessary, in an economic sense. to lighten the structure, especially when the airplane is a large, manypassenger type. This, for structural reasons, entailsreduction of the maximum possible pressure difference, as between cabin pressure and external pressure. .This also requires the provision of automatic controls to insure that never, under any circumstances, will this selected differential of pressure be exceeded, whether the tendency to exceed it may arise from an excessive rise or rate oi rise of cabin pressure or from an excessive drop or rate of drop of external pressure. To exceed this selected differential-the value of which is primarily determined by structural and economic considerations, and which may vary in different designs-would subject the structure to bursting stresses in excess of those for which it is designed, with possibly permanent structural damage.

In any attempt to control the pressure within such cabins it must be borne in mind that iiowthrough, or, in other words, ventilation, is an essential consideration. While pressure must be maintained within the range of physical wellbeing and of reasonable comfort, this alone would not serve to make high-altitude flight practicable. Stale air must be continuously or frequently discharged, and fresh air must be admitted to supply the loxygen which is consumed, in addition to the maintenance oi adequate pressure.

Likewise. rate of flow is an important consideration. Too low a rate of ilow is, of course, a concomitant of lack of adequate ventilation; too high a rate of now is also undesirable, for it pro-V duces drafts.

Infiow and outow must be properly balanced. and the extent and manner of this balance is dependent upon various factors. including altitude and absolute cabin pressure, and the rate oi ilow through the cabin. 'I'he inow rate must not be so rapid at low or medium altitudes that outilow and flow-through, or ventilation. are at such high rates as to be objectionable, yet the inflow rate must be sufficiently high at high altitudes to supply adequate amounts oi' the comparatively rarefled air to maintain adequate cabin pressure. This implies variable controllor regulation of the inilow rate. The outflow rate likewise must be variabiy controlled, for a relatively high'outow rate is necessary at low altitudes to avoid supercharging, but the outow rate must progressively decrease with increase of altitude through the medium altitude range. and thereafter the rate of outiiow may increase somewhat throughout the range oi operation at the limiting diil'erential of pressure. Itis clear that the inflow rate must be controlled, and that the outilow rate also must be controlled. Either in their design or by some interconnection the controls of outow and o! inflow must be coordinated and balanced under all conditions. In the present arrangement the two are physically and functionally interconnected, yet it must 'be remembered that this is only one way of accomplishing the necessary balance.

and that other ways of balancing or o! operating these controls are not outside thezscope nor the spirit of this invention.

to the comfort of a passenger. The eilects of tooV rapid a rate of change are well-known to air travelers, and custom or regulations prescribe the maximum rate of ascent and descent ot passenger-carrying airplanes. It is immaterial how slowly the pressure is changed, unless, by lagging behind the actual rate of change of external pressure the cabin pressure may equal or tend to exceed the selected difierential. In auch a case it is imperative that suitable controls automatically prevent exceeding such differential.

It is known that, ii the rate oi ilow is properly controlled, so that it is not excessive nor yet too slow for adequate ventilation, and if the rate of pressure change is controlled so that it is not so rapid that passengers will be unable to adjust vthemselves to it. pressures appreciably lower than sea level pressure can be borne without noticeable effectswithin certain limits, of course.

The present invention relates to the control oi pressures within such a cabin in a manner to pro` duce the minimum of deleterious physiological effects; to protect the structure against excessive internal, outwardly directed stresses, or any external inwardly directed stresses; to the end that the total weight and cost of the airplane may be kept to a minimum, to insure adequate ventilation, yet to control the rate of flow, both into and from the cabin, and the rate of change of pressure, as necessary; to counteract the eifect of leakage from the cabin or of failure of the supercharging system; to provide adequate automatic controls for the inlet and discharge of air, and to balance the inlet and outlet flow controls one with the other; to provide automatic indicating or operating mechanisms, as a result oi the operation of which the system is adjusted to fit conditions present or immediately to be encoun tered; to lessen the likelihood of failure of the system due to ice formation, to conserve to the greatest degree heat within the cabin when needed; and to provide a system whereby temperature conditions within the cabin will automatically be maintained substantially constant regardless of low external temperatures, particularly noticeable at high altitudes. meant any habitable space within an aircraft, or any like space which must be kept at an elevated pressure to prevent damage to contained persons or objects. In certain military aircraft a "cabin" may be a mere cell for occupation by a gunner.

Speaking functionally, it is an object to provide a system of the character indicated, and a control mechanism, so arranged that, while maintaining adequate ventilation, the pressure difference between cabin pressure and external pressure may be permitted to increase, primarily by decreasing the cabin pressure in general correspondence with but more slowly than th'e decreasing external pressure attendant upon an increase in altitude, until the selected differential of cabin pressure in excess of external pressure isr reached. whereupon the differential is or may be maintained, but automatically is never permitted to be exceeded, as the external pressure drops, up to the limit of the capacity of the source (usually a supercharger) which supplies air under pressure to the cabin. In its broad aspect, I have provided a combination of Ventilating and pressure controlling means, wherein there is means to increase the cabin pressure above external atmospheric or ambient pressure, and a means which automatically, and in all circumstances, prevents this cabin pressure from exceeding a predetermined differential.

In the specific arrangement illustrated, the cabin pressure is permitted to drop generally in accordance with the pressure altitude curve, up to a given altitude; the cabin pressure is then maintained substantially constant, at a value corresponding to that selected altitude, or is permitted to drop by only a small amount, notwithstanding that the aircraft gains in altitude and the external pressure drops materially, until a given pressure differential between the internal and external pressures is reached; the selected pressure diil'erentiai will thereafter be automatically maintained, as the altitude increases. Thus as the aircraft takes oil from a landing field which is at an altitude below the ilrst critical altitude, the cabin pressure will drop in accordance with (though possibly at a value slightly in excess of) the pressure altitude curve of the outside atmosphere, to a selected altitude, then will be maintained nearly constant to a higher altitude, then will be kept at a constant differential By "cabin is above the outside pressure. the absolute pressure dropping continuously but at the same rate as the external pressure drops, until the limit of the capacity of the supercharging system is reached, the system being arranged to give an indication at this point that this limit has been reached. In descending the operation is merely reversed, and the cabin pressure curve retraces itself.

It is an object to provide in such a system pressure-sensitive elements serving to operate the system automatically, but preferably, though not necessarily, to a certain degree under the control of an attendant, one such pressure-sensitive element being subject to absolute pressures, preferably that obtaining within the cabin, and the other, always automatically operable being subject to differential pressures between the interior of the cabin and the outside atmosphere. It is an associated object to arrange the two control elements, such as the absolute-pressure control and the overriding differential-pressure control, respectively, to actuate a common now-control device, such as the outflow valve, under conditions which require cabin pressure in excess of external pressure. It is also an object to provide servo mechanism in association with the elements men tioned, and in such a system, connected to be controlled by the pressure-sensitive elements referred to above, and in turn controlling such flowcontrol device, and other similar or associated devices.

It is a further object to provide in such a system inlet and outlet flow valves which will automatically operate to prevent insuilicient pressures `within the cabin by admitting outside air should the external atmosphere tend to increase over the internal pressure, or by preventing discharge of air to the exterior should the internal pressure drop unduly. 'I'he system is also arranged so that it will automatically prevent discharge of air from the cabin in the event of failure of the supercharging system, and it is further so arranged that the cabin may be sealed off manually should the automatic controls fail to function.

Enough has been said to indicate the general purposes of the invention. It will be better understood as this specification progresses. and further objects will be ascertained in the course of the specific description of the system.

My invention comprises the novel system, and the novel parts thereof, and their relative arrangement, as shown in the accompanying drawings in diagrammatic fashion, and as described- 4 in this specification and more particularly defined by the claims at the end of the same.

The accompanying drawings are diagrammatic only, and illustrate a typical system as applied to a passenger; airplane intended for high altitude travel.

Figure 1 is a perspective view, showing parts of such an airplane cabin, wing and engine nacelle in shadow view, and illustrating the relationship of the parts of the system to each other, and to the airplane. y

Figure 2 is a general sectional view through the principal controlelements of such a system, and Figure 3 is a similar View' of a control valve, normally manually operable, on an enlarged scale and in a different position from that shown in Figure 2. v

Figure 4 is an elevation of the supercharger and heating arrangement and its controls.

Figure 5 is a diagram of the alarm or signal Figure 6 is a graph or the pressure altitude asma 3 curves. normal and as attained by the use oi my invention.

Figure '7 is a section through the control valve, in a position corresponding to Figure 2, but showing a modified form.

The system as a whole is illustrated in Figure 1. A supercharger 9 ls intended to typify any convenient source of air under pressure. As shown, it is connected to the engine, to be continuously driven thereby, and at a rate which is substantially constant, These details, however. are purely illustrative, however, and are not intended to be restrictive. Such a supercharger receives air from a convenient source, as from a scoop or ram properly located in a pressure area, as usual, and delivers this air through a conduit 90 and preferably past a heating arrangement, indicated as taking the form oi a' surface of the wing near its trailing edge. As

an alternative or supplementary supply and flischarge system I may provide a conduit 91, the forward end or ram of which is located in a pressure area. for instance at the nose of the cabin. to scoop in or admit air, and to discharge it within the interior of the cabin through ouilets (not shown), and air may be discharged from the cabin through a conduit 98. which has registers or inlets 99, and which terminates .in a low pressure area, for instance at the tail of the fuselage. Provision may be made for connections from one or the other, or from both. of the supply conduits 92, 91, as for example bv the branch 91' from the conduit 91. to suppl" air to individual ventilators (not shown) placed adjacent the passenger seats, and adapted in he opened and closedby the passengers as desired. and as is now customary in passenger airplanes. It will normally be desired to heat the air, at least that which enters from the super-charger. since the atmosphere at appreciable altitudes is likely to be cold, and it will not be suillciently warmed in many cases by the compression given it by the supercharger. The heating rancement is separately patented, Patent No. 2,193,141, issued March 12, 1940, and it need only be peinted out here that water is led as needed from a water tank 8 through a boiler 8i disposed within the exhaust stack 80 of an engine (not shcwnl or is otherwise arranged to be heated. and thus steam may be generated to be supplied to the condenser 9|, and the operation of this heating arrangement is under the control of a valve 82 controlled by a thermostat B3 located conveniently, as for instance in the interior of the cabin. Should it be necessary to absorb heat from the compressed air, an intercooler `of known type (not shown) may be arranged in known manner in the conduit 90.

Normally the air forthe interior of the cabin at low altitudes will be supplied in part through the conduit 91, past a valve 1, and the discharge from the conduit 98 will be controlled by a valve l0. These valves are preferably connected'i'or simultaneous operation, that is to say, both may be opened or both may be closed at one time. For instance, the valve 'I is operable by a solenoid 1i and the valve 10 by a solenoid 12. and these solenoids are controlled manually or automatically by or in accordance with pressure-sensitive devices and alarms, which will be later described in detail. It is sutllcient to point out here that up to 8000 feet, for instance, the valves I and lll may be left open, and an alarm is given at this pressure altitude as a signal for an attendant to close these valves, or the alarm-actuating means may automatically close them. There is a further alarm or the same alarm may be used in another circuit, whereby a signal is again given at a considerably greater altitude when the limit of the capacity of the s'upercharging system is approached.

By reference to Figure 6 it can be seen that the normal pressure altitude curve, shown in dash lines, is one which drops from a point in the vicinity of 30 inches of mercury at sea level to a value in the neighborhood of l2 inches of mercury at 24,000 feet. With the conduits 91 and 98 open at sea level, and from thence up to 8,000 feet (or any similar ilgure arbitrarily selected), the pressure altitude curve within the cabin will approximately coincide with the -external pressure altitude curve, and ls shown between points A and B oi the graph, Figure 6, in

solid lines.` The pressure within the cabin may slightly exceed the external pressure for any given altitude because lt will be remembered the super-charger is operating continuously, but by a mechanism within the control unit M and to be described hereafter the control unit M. at these altitudes, is arranged to regulate only the rate oi now from the supercharger into the cabin. Between points A and B, the latter approximately 22 inches of mercury, actual supercharging of the cabin is not necessary because normal atmospheric pressures up to 8,000 feet altitude are not physiologically harmful. and, furthermore. it is quite possible that landing fields will be f used which are at altitudes up to this ilgure.

Thus between stations A and B the automatic control unit M is so arranged and set that it has no control function except to regulate the rate of flow from the supercharger.

I do not mean to infer that the `cabin pressure may not be permitted to drop at a rate less than the rate of external pressure drop: in a copending application, Serial No. 216,028. filed June 27, 1938, I have disclosed how this may be accomplished. In the simple arrangement herein disclosed it is more convenient and understandable to permit the cabin pressure to follow one speciilc curve, whether it is rising or falling, and this curve nearly, if not quite. coincides with the pressure altitude curve of the external atmosphere, below 8000 ieet, that altitude se- .lected to accord with arbitrary design considerations.

Pressures lower than that obtaining at 8.000 feet commence to become uncomfortable and to produce undesirable, if not harmful, physiological effects, especially on passengers unused to such altitudes, and accordingly it is desired to maintain substantially constant pressure from 8,000 feet upward at least within the capacity oi' the structure to resist internal pressures greater than those outside. Thus between points B and C on the solid line of Figure 6, that is, from about 8,000 feet to about 16,000 feet, the pressure inside the `cabin is maintained substantially constant,

though the external pressure is continuously decreasing with increase in altitude. There may be some pressure drop between stations B and C, as indicated at X. It is not large from the physiological standpoint, but is suilicient to eiiect operation of certain control devices Within or associated with the unit M.

At the altitude corresponding to point C, here shown at 16,000 feet, a differential pressure exists between the inside and outside pressures, and this differential is so chosen as to be safely within the structural limits of the cabin, but it is not desired to exceed this differential. .Accordingly when a cabin pressure corresponding to the point C has been reached, automatically the control unit M is placed in condition to maintain from this point onward, with further increase oi' altitude. not a uniform cabin pressure but a uniform differential of pressure between the inside and outside, and thus from point C to D, the latter at, for example, 22,000 feet, the differential pressure is maintained constant, although the absolute pressure within the cabin drops. This differential pressure may be, for instance, 2V.: pounds to the square inch. Though no alarm is shown, arranged for operation at point C, and none is needed because the system automatically maintains the dierential from point C onward, an alarm might be provided, and the changeover from constant-pressure conditions to constarrt-differential conditions might be manually accomplished by an attendant attracted by such a signal.

Beyond some given point, as the point D, the cabin pressure diiTerential can no longer be maintained with the capacity of the supercharger selected, although, of course, with a supercharger of different capacity the point D will be differently located. The differential begins to decrease, as is shown by a downwardly trending solid curve from D to E. At point E an absolute cabin pressure is reached, which tends to be physiologically detrimental to the occupants of the aircraft, and at this point it is arranged that a signal shall be given to indicate the attainment oi this altitude, and the dropping of' internal pressure to this point. This signal indi- Cates to the pilot or attendant that the cabin pressure is too low, and that the aircraft should descend or arrangements should be put into effect immediately to supply emergency oxygen. This signal may be supplanted or supplemented by automatically operable means to initiate such oxygen supply.

The above indicates the aims whichare attained by the system which will now be described in detail. Pressures and capacities and altitudes are arbitrarily selected, and may be varied at will, all as will be evident to the aircraft engineer, but those selected will be used i'or purposes of illustration. Also while I shall proceed to describe the control devices in detail. it will be understood that the arrangement described is chosen purely for purposes of illustration. and that various changes may be made in the form. character, and relative arrangement oi' the parts without departing from the scope of my invention, as defined in the claims.

In the arrangement which I shall proceed to describe and which is shown in Figures 2 and 3, a supercharger supply conduit 90 has in its line an inflow valve I which controls the dow from the conduit 80 to the cabin inlet conduit 02. Flow from the cabin is through an outlet Il and passage 96, past an outflow valve 2. Each of these valves is operable through the medium oi a servo piston, the valve I being operable by the 'piston Il and the valve 2 by the piston 2t,

In the arrangement shown the inflow valve il is largely controlled or balanced by the outflow' valve 2 by now sensitive devices, which will described in detail hereafter. It may be pointed out that the outflow valve 2 is controlledi pri.- .marily and selectively by two pressure-sensitive devices, and thatV these pressure-sensitive devices operate only upon the outflow valve. One oi these pressure-sensitive devices is an absolute-pressure sensitive device, taking the form in the present illustration of the evacuated Sylphon bellows 2i, with a spring 2 I resisting its collapse. The other pressure-sensitive device is a differential-pressure sensitive device, represented as the Sylphon bellows 4, which, through means that will be described in greater detail, is subject to the pressure difference between the interior of the cabin and the external atmosphere.

The servo pistons I3 and 24 and a further control piston II, the purpose of which will appear hereafter, are each subject to a pressure difference at their opposite faces, and are sufilciently loosely fitting in their respective cylinders that a measurable amount of leakage is inevitable, is expected, and is depended upon for the proper functioning of the piston, and to maintain` equilibrium in each position, between the forces act ing at opposite sides of the pistons. Taking the piston 24 as typical, the actuating pressure diiference is developed by subjecting its under side to supercharger pressure by way of the passage 25. and by permitting air which leaks past the piston to its upper side to escape, either by way of the passage 26 or the hollow stem 22, to a lower pressure space, and inthe present arrangement to the lower pressure of the external atmosphere which obtains at all altitudes. Escape via 28 is controlled by a valve 42, as wil appear later. Escape via. 22 is controlled by stem or spindle 21, acting as a valve with :f the end of the hollow stem 22, and c a manner which will appear more iu r If the stem 21 is but slightly removel a few thousandths of an inch) from the end or the hollow stem 22 (assuming valve iii to be closed) escape of pressure from above the piston 24 can be so slow as to he at a rate but slightly greater than the rate of leakage past the fiston from below. The pressure above the pister-i .is Just suiiiciently less than the pressure belge the piston that the weight of the piston-vane assembly is equalized, and no movement occurs. Parts are then in equilibrium. If now the stem 21 be more greatly removed from the end of the hollow stem 22 escape ol' pressure to atmosphere through the latter is Vmore rapid than leakage from below the piston. Equilibrium is destroyed and upward movement o1' the piston occurs. Immedlately it moves upwardly it tends to close the space between the upper end of the hollow stem 22 and the stem 21, and the upward movement stops, unless, indeed, the stem 21 continues to move upwardly. On the other hand, if the stem 21 moves closer to the end of the hollow stem 22, escape of pressure from the upper side of the piston is not at as rapid a rate as it can be replaced by leakage from below, and upon approximate equalization of pressure above and below the piston the weight of the piston-valve assembly causes the latter to move downwardly. Immediately. in this case. the downward movementor the upper end oi the hollow stem 22 casca removes it more greatly from the stem 21, low

pressure again has access to the upper side of the piston, unless, indeed, the stem 21 continues to move downwardly, and downward movement of the piston valve assembly is stopped in a new position of equilibrium.

The nal outlet 93 from the cabin preferably is in heat exchange relationship to the inflow conduit 30. The air in its passage from the conduit 30 to the conduit 32 is led around or adjacent to the cabin outlet 83, thereby to warm the' latter, due to the heat o! the air heated 'by compression and owing to the cabin. In this manner icing conditions are prevented which might tend to clog the cabin outletI 98. On the other hand, if the discharge air should be warmer than the cabin inlet air, which is unlikely, this arrangement tends to absorb any latent heat from the air being discharged, to return it thence to the cabin.

The ilow control mechanism centers around a control valve 3, which in the present disclosure is manually operable by the handle 30, but which may be arranged for automatic operation under pressure control, for instance, and around a cabin inlet Venturi throat Ill and a cabin outlet Venturi throat 20, arranged for selective control of the piston Il through the valve 3. The function of the ilow control mechanism is tocontrol the rate oi iniiow to the cabin at low altitudes primarily under the inuence of cabin inlet flow conditions (see Figure 3), and to control inflow at medium altitudes primarly under the innuence of cabin outlet tlow conditions .(see Figure 2). f

The control valve 3 is provided with two passages 3I and 32, terminating in four ports, adapted to register with four of six pipes connected to the valve casing. These pipes are numbered 33, 3l, 35, 36, 31, and 3B. The two alternative positions of the valve 3 are shown by comparison of Figures 2 and 3. The position of the control valve shown in Figure 2 is that assumed for operation at medium altitudes. that is, over 8,000 feet, and movement of the inilow valve I is under control of the piston I I, acted upon by outlet flow conditions through the venturi 20, acting through the pipe 3B, the`valve passage 3l, and the pipe 33 upon the under side of the piston Il. Upon its upper side the piston II is acted upon by the cabin static pressure communicated through the pipe 35, the valve passage 32, and the pipe 36 to the upper side of the piston.

As has been pointed out. this piston nts loosely' within its 'cylinder so that air gradually leaks past the piston from its higher pressure side Vto its lower pressureside, tending to equalize such pressures. Movement of the'piston in a direction to open the valve is assisted by a coil spring |03. Counterweights I2 maybe employed, if required, to prevent motion of the piston under the iniluence of inertia eilects, from heaving or other accelerations oi the aircraft in rough air. Counterweights 23 serve a like purpose with relation to the piston 24.

The servo piston I3 is similarly loosely tting within its cylinder. Its under side is connected through a pipe I4 with the atmosphere, and its upper side is also in` communication with the atmosphere through a pipe `I5 past a check valve I3. However, provision is made, under most conditions, to aord a certain amount of access of supercharger pressure within the conduit 30 tol the upper side of the piston' I3. Such access may be had by making the stem I1 of the valve 15 Like the inlet valve I, the outlet valve 21s sub- I hollow, the stem I1 and its hollow bore terminating at their upper end immediately above the piston I3'and 'within the cylinder chamber which is above this piston, and at their lower end within the conduit '30. The lower end of the -bore is normally closed to a certain degree by a separate stem or spindle IB which is movable with the piston II. In addition the valve I may be controlled manually for closing in opposition to any and all automatic controls and forces by a handle I3 which functions through a stem I3' bearing upon the upper end of the hollow stem I1. This permits closing of the valve I to prevent excessive supply of air into the interior or the cabin in such an emergency as would result from the failure of the flow-sensitive mechanism to function or breakage thereof.

In the position of the control valve 3 which is shown in Figure 3, which represents the position of the valve below 8,000 feet, the lower side of the control piston II is in communication with the cabin inlet ilow pressure at the throat of the venturi III through the pipe 3l. the valve e 3l, and the pipe 33, whereas the upper side oi the piston II is connected through the pipe 31,

the valve passage 32, and the pipe 33 with the inlet at the pressure side of the inlet venturi I0, so as to be under the iniluence o! the cabin inilow, which latter primarily controls `the piston I I at this time.

The functioning of the control piston II is substantially the same in either position of the parts, that shown in Figure 2 or that shown in Figure 3, and the principal diilerence is that in the one case the initiation of control is under the influence of cabin outow (Figure 2), and in the other case (Figure 3) the control is under the influence of `cabin inflow. In either case the space above the control piston II is connected to a pressure source and the space therebelow is connected to a suction source. The pressure differential thus created acts downwardly, but is balanced by the spring |03. Leakage past the piston is calculated to be just suilicient, under proper operating conditions, to hold the piston ii and its spindle I3 adjacent, but not quite in contact with (a spacing oi a few thousandths of an inch) the lower end of the hollow stem I1, provided the steinl I1 and its valve I are in the proper position, under the conditions then existing, to balance inilow with outflow. At this spacing supercharger pressure or inlet ilow pressure is admitted through the hollow stem I1 at such a rate that by leakage upward to the lower side of piston I3,'which is in free communication through I4 with the lower atmospheric pressure, the piston valve assembly I, I3 is balanced against the forces (largely gravitational) tending to close the valve I. It the forces acting upon the control piston II cause this to move downwardly, more supercharger pressure is admitted through the hollow stem I1, due to separation of the upper end of the spindle I3 from the lower end of rthe stem I1, and pressure is thereby admitted ject to certain controls, and is moved by a servo device. The evacuated Sylphon 2l, which is an absolute pressure-sensitive device, is operable under the influence of the differential between two oDDOsed forces. One such force is the spring 2|',

' tending to lessen the space between the spindle 21 and the upper end of the hollow stem 22, and thereby, through the servo piston 24, tending to close the valve 2. The other such force a variable, is the cabin static pressure tending to collapse the bellows 2| and thereby withdrawing the spindle from the hollow stem 22, and reacting through the servo piston 24 to permit opening oi' the valve 2. Movement of the valve 2 is also controllable by the differential-pressure sensitive bellows 4, having within it a compressionresisting spring 49, and internally in communication, vla pipe 43, with the external atmospheric pressure. This bellows is enclosed within a housing 40, which through a pipe 4l is in communication with the cabin static pressure, so that externally the bellows 4 is under the innuence of cabin static pressure tending to compress it, and upon its compression to open the valve 42. The spring 49 is of such strength that opening of the valve 42 does not occur until the selected diilerential between cabin pressure and external pressure has been reached. Upon opening the valve 42, communication of the space above the servo piston 24 with the external atmosphere is under control of the valve 42, for the hollow stem 22 is closed, at all cabin absolute pressures lower than C, Figure 6, by the spindle 21. Forces developed under differentialpressure control are sufllcient to move the spindie 21 upwards, against spring forces urging it downwardly.

The pipe 26 under such conditions admits external atmospheric pressure to the upper side o! the servo piston 24 under control effected by the valve 42, under the iniiuence of the dlilerentialpressure sensitive device 4. Externally, then, the bellows 4 is under the innuence of cabin static pressure tending to compress it, in opposition to its spring 49, and upon its compression to open the valve 42, and internally the bellows 4 is in communication through a pipe 43 with the outside atmosphere at a pressure below that of the pressure cabin, and a branch 44 of this pipe communicates past the valve 42 with the pipe 26. When the cabin differential pressure tends to exceed the desired maximum, whether from increase of absolute cabin pressure or from drop in the external atmospheric pressure, the bellows and spring yield and compress, allowing the valve 42 to be raised from its seat. When this occurs the pressure diilerential at the opposite sides of the servo piston 24 is destroyed, as has already been explained, and corresponding opening movement of the valve 2 automatically occurs, relieving any excess of pressure. If cabin ditferential pressure tends to drop below the set value, a reverse action occurs, the valve 2 moves towards its seat, and the desired dinerexitlal is restored automatically.

In addition to or in conjunction with Vthe control devices Just described, and which are generally indicated in Figure 1 at M, there are barometric control or indicating devices within the cabin and subject to the pressure therein, shown in detail in Figure 5, and in Figure 1 at Y. It has already been noted that the inlet valve 1 and outlet valve in the open or rammed air supply and discharge lines, respectively, are condoubly wound solenoids 1| and 12. There is provided. as part of the control at Y, a pressuresensitive Sylphon 5 which is so arranged as to close the gap between terminals 5| in an electric circuit when a pressure altitude within the cabin is reached which corresponds to 8,000 feet, provided that a switch 52 in the circuit is properly closed, that is, is in contact with terminal 51 in the full line position shown in Figure 5. This isthe normal position of the switch arm up to 8,000 feet. At 8,000 feet it is desirable to close the valve 1 and 10, and to throw the control device M into operation to maintain constant pressure between the points B and C of the graph Figure 6. Accordingly, upon energization of the signal 54, an attendant throws the switch arm 52 into contact with the terminal 53. This signal or alarm B4, i'or instance a light, is energized when the pressure-sensitive element 5 closes the gap between the terminals 5i, one of which connects with the terminal 51, thereby completing a circuit through the alarm or signal light 54; When the attendant throws the switch 52 into contact withthe terminal 53, the solenoids are so energized as to close the valves 1 and 10, and the switch E2 may be so connected that it throws an arm 39, connected to the control valve 3, into such position as to move the control valve 3 into the position of Figure 2. To this end the arms 52 and 39 may be both secured `to a common rock shaft, as shown in Figure 5.

It may be noted here that* in order to 'open the valves 1 and 10 it is only necessary to throw the switch 52 into contact with the terminal 55, and this motion will turn the control valve 3 into the position oi Figure 3.

After the switch handle 52 has been thrown into contact with the terminal 53, and the valves 1 and 10 have been closed, if it is thrown to a neutral position the signal light 54 is no longer illuminated. Such a neutral position may be intermediate the terminals 53 and i1. However, a second pressure device 50, similar to the element 5, is part of the control device Y, within the cabin, the element 50, however, being arranged to close a circuit through the terminals 56 when the pressure altitude reaches 16,000 feet. This is not the actual altitude, the latter being considerably higher, say 24,000 feet, but since the element 50 is within 'the cabin it is arranged to operate, regardless of the position of the switch arm 52, when the cabin pressure corresponds to the external pressure at 16,000 feet. This again closes a circuit through the signal light 54, indicating that the point E has been reached. and that the pressure has i'allen to a point where additional oxygen should be supplied. The element lil might instead be arranged to close the circuit at the point C; or at the point D on the graph, Figure 6, or there may be .several such elements operable at diilerent pressure altitudes. It will be borne in mind that the light 54 is an example of an electrically energizable device which is energizable at selected pressure altitudes -by the different pressure-responsive means, and it may as weil indicate automatic means to efiect movement oi' valves or control devices, or

auxiliary -oxygen supply devices, although it is l action.

*roliable under the influence oi' the respective n The operation o! the system will be best understood by following through a typical series o! actions. As previously noted, Irompoints A to 4B of the graph cabin supercharging is not occurring, because the valves I and 10 are open to equalize internal and external pressures, since normal atmospheric pressures up to 6,000, 7,000 or 8.000 feet are not physiologically harmful or discomiorting to passengers. The control valve 3, in the position `of Figure 3, controls the rate of flow from the supercharger into the cabin, under the influence o! the inlet venturi IB. From point B to point C, where the cabin pressure is maintained substantially constant, the valve 3 is in the position of Figure 2 and the cabin supercharging control device M regulates the rate of ow from the Vblower into the cabin, under the influence of the outlet venturi 20.

With the control valve in the position oi' Figure 3 the upper side or the piston Il is subjected to inlet pressure through the pipe 3l. Any decrease in pressure effected by increased now past the Venturi meter IB is carried through the valve 3 to act upon the lower side of the piston Ii, evacuating the lower portion of its cylinder laster than air can leak thereinto, past the loose piston from the high pressure side, thus tending to move the control piston downwardly. Accordingly any tendency for increase in inlet flow will cause the piston to be deflected downwardly, acting as previously described to close the inlet valve I, and thereby to reduce the rate of inflow. A decrease in ilow through the venturi I will cause the piston II to move in the opposite or upward direction under torce of the spring |00, opening the valve I. Therefore, from A to B, constant dynamic flow is provided at the cabin inlet from the supercharger, regardless oi.' the speed oi the impeller of the latter. Instead oi' controlling rate of inflow, the same or similar controls might vary the speed of the supercharger. to the same end.

Dependent upon particular weather conditions the inlet valve 1 and outlet valve 'III controlling the open or rammed inlet and discharge, may be either opened or closed. Let us assume that these valves are both open to some degree, according to the requirements oi the passengers. When point B is reached the pressure-sensitive element 5 energizes the alarm or signal El, indicating to the attendant that vcabin supercharsing should sumcient to cause complete expansion oi' the Sylphon 2|, and consequent complete closure oi the outlet valve 2. As previously pointed out. the actual force for the movement oi the valve 2 is not supplipd directly by the stem 21, movable with the Sylphcn 2|, but by the servo piston 24. Thus starting at point B of the graph, ii' for any reason the cabin pressure tends to drop, the Sylphon 2| will expand under the inuence ot spring 2|' and will act through the servo mechanism to close the outlet valve 2. Any tendency for the pressure in the cabin to increase from the point B upward will reverse the process, such excess pressure overriding the resistance o! the spring 2 I Occurrence of a leak in the cabin will tend to cause a drop in cabin pressure. The small increment oi drop causes a relatively large degree or closure of the cabin outlet valve 2; consequently there ls a tendency for the flow to be abruptly reduced through the outlet 98. 'Ihe consequent reduction of ilow in the oulet venturi 2|) brings the inlet valve servo mechanism to a new position of equilibrium, providing a greater and ,compensating ilow past the inlet valve I.

Accordingly even a very large leak in the cabin will cause a negligible drop in cabin pressure, and an appropriately increased ,supply of air from the cabin supercharger to resist any drop in the cabin pressure. 'I'he supercharger is allowed to overload during the presence oi such conditions.

At point C oi the graph a cabin supercharging condition is reached such that for structural reasons it is not desirable to further increase the diierential pressure between the cabin and the be started. Accordingly the switch handle 52 is moved manually (or automatically, as suggested above) from terminal Bl to terminal 63. to cause closure of the valves 1 and Il), breaking the circuit through the light il, and as the switch handle approaches the end of such movement its motion is transmitted through the levers 39 and 30 and linkage 39 to the control valve 3, to reverse the latters position. For control purposes this throws the* sensitivity to the ow'previously under the influence oi' the inlet venturi I0, to the outlet venturi 20. 'I'he valve is now in the position of Figure 2. Accordingly the cabin inlet4 valve I is regulated in the same fashion as previously described, but under the control o! the outlet venturi. Y

At point B in the graph, which we have now reached, the pressure of the extemal atmosf phere, which is substantially the same as the pressure within the cabin, is no longer sumcient. to hold the absolute pressure-sensitive Sylphon2| collapsed to its limit, for the collapsing ioroe has decreased, while the opposing spring force has re mained unchanged, and the Sylphon commences to expand due to pressure from the spring 2|' within it. 'I'he degree of this expansion is abrupt, and dependent upon the pressure drop X from point B to point C. This pressure drop X is not atmosphere. Accordingly ,the differential pressure responsive element I is so arranged that it commences to compress under the differential between the higher cabin static pressure, to which it is subjected exteriorly, and the lesser atmospheric pressure to which it is subjected internally. Compression of the element 4 admits atmospheric pressure past the valve 42 to the upper side of the discharge valve servo piston 2l. This causes automatically opening of the discharge valve against the will of the absolute pressure responsive Sylphon 2|, in effect overriding the latter, and thus from point C to point D of the graph. and without any action by the attendant, a cabin diierential pressure of, for example, 2li/2 pounds per square inch, is maintained. The rate of ilow to the cabin under control o! the outlet venturi 2li may still remain constant, for as the outlet valve 2 opens, tending to increase the outflow, the yinlet valve will tend to open. The two automatically maintain their balance. Y At point D of. the graph the limit of the supply characteristic of the supercharger is reached, and itcannot maintain any longer the desired pressure differential in the cabin, and the cabin inlet valve I is then fully open. Be-

- yond point D the 2% pound cabin pressure dirlarge from the physiological standpoint, but is Ierential can no longer be maintained, and the ditlerential tends to decrease. Ai; point E of the graph a cabin pressure is reached which is physiologically Adetrimental to occupants oi Athe cabin. This, through the pressure-sensitive element 50 or a similar element, causes energization lof the alarm or signal El, and this is the signal to the attendant that the pressure of the cabin lise.

It is to be remembered that the operation represented by the graph, Figure 6, is not the only manner in which the control may operate. By suitable design or adjustment of the absolutepressure sensitive unit, or its spring 2I', the location of the point B (that is, the altitude at which supercharging `commences) can be altered; if the spring is made sufficiently strong, supercharging can commence at sea level; with a weaker spring supercharging begins at a higher altitude. In similar fashion, by suitable design or adjustment of the differential-pressure sensitive unit, or its spring 49, the location of the point C can be altered; for instance, with a stronger spring a greater differential must exist before the valve 42 is lifted from its seat, and

this has the effect of shifting the line C-D-Ey farther from the approximate atmospheric line A-B, extended.

Since supercharging, as shown above, can commence at any selected altitude or external pressure, and since the absolute value thereof is, in effect, dependent upon the strength of a spring, it is possible to vary that value during ascent, at a rate which may be related to time, or alternatively to rate of change of external pressure, by a progressive adjustment. Always the cabin pressure bears a predetermined relation to external pressure, whether that relation be equality. A to B, whether the one exceeds the other by a given increment, C to D, or whether the one changes at a rate which is a given ratio to the rate of change of the other, B to C. These relationships, therefore, are each susceptible to change, and such change can be continuous during flight.

For instance, knowing the intended time rate of ascent and consequently the intended time rate of atmospheric pressure drop, the adjustment of the force of the spring 2|' can be made at a related time rate. This would have the effect of increasing the cabin pressure difference over atmospheric pressure for each time unit (minute) of ascent, and the curve would trend upward away from A-B. It would be a steady divergence if the actual rate of climb coincides with the intended rate of climb. Instead of effecting such adjustment under the influence of a time factor, it could be effected under the influence of a pressure factor, such as a rate-ofclimb element, and then, if the actual rate of climb did not follow the intended rate, the increase of the cabins pressure difference over atmospheric pressure would actually occur at a rate corresponding to actual change of altitude. The curve would then trend steadily away from the atmospheric curve A-B, and the ratio oi cabin pressure difference over atmospheric, to total atmospheric pressure change from sea level, or from some other selected datum, could be the same at all altitudes. Of course, the selected limiting differential, controlled by 4, is never exceeded.

It is also the function of the alarm system of Figure 5 to warn the attendant if the supercharging system is not working properly between points C and D. Thus if a leak of very large proportions should have developed in the skin of the aircraft the warning would be given, since the pressure differential would not be maintained. -Also any mechanical difilculty in the supercharging or control `system resulting in a reduction of cabin pressure below a 16,000 foot pressure altitude would be indicated.

Other conditions in the nature of emergencies may be similarly indicated by the same or other signal devices. For instance, an excessive or insufficient rate of air supply or excessive cabin pressure might be similarly indicated.

During supercharged operation from'point B of the graph on through points C and D provision is also made in the control unit for prevention of loss of air from the cabin in the ease of complete failure of the supercharger or ci?V the supercharger supply conduit 80. Should any such conditions occur, the inlet valve I is returned to its seat by the dynamic effect of reversal of flow at the inlet. The cabin pressure' at such a time is in excess of the atmospheric pressure 'and tends to iiow outwardv past the valve I and through the conduit 9B, and this tendency to outflow closes the valve I. Under this condition of reversed flow tendency past the valve I, outlet valve 2 conditions will be such that the stem I8 will be allowed to close the hole ln the stem I'i eliminating differential pressure across the piston I3, again by reason of leakage around and past this piston. The check valve IB further insures that the pressure above the piston I3 will not be brought to a lesser value than that below the piston I3, which latter condition would tend to cause opening of the valve I during reversal of iiow past it. The same is true as to the outlet valve 2, since the supercharger pressure through 25 is no longer available to resist its closing. Furthermore, the valve I may be forcibly closed by the manual lever I9,

in the event of failure of the supercharger or to prevent any excessive cabin pressure resulting from malfunctioning of the control unit.

Both the inlet and outlet valves I and 2 are also capable of acting as inlet relief valves. Thus if the aircraft had been operating in the region Indicated by point D, Vand were suddenly brought to a lower altitude it would not be possible for the atmospheric pressure to exceed that of the cabin, for this excessive atmospheric pressure would merely force open the valves I and 2, thereby equalizing the pressure within the cabin and that outside it. This would occur even though the supercharger or the pressure-sensitive mechanism in the control Vunit had become inoperative. l

A further modification of the control valve I is preferable in some instances, as when the blower or such other cabin air supply device is particularly changeable in discharge pressure or is very unstable. This would be offensive in a comparatively large pressure cabin since, during operation from points B to D in Figure 6 while the average cabin inflow and outflow might be kept very constant, there might still be rather small flow variations of relatively high frequency permitted at the cabin inlet, falling above and below the average inlet flow value.

I prefer, therefore, to temper the flow control in such cases, between points B and D, by allowing the inow metering system to slightly influence the position of the valve I, while he predominant influence is still derived from the outiiow metering system, and all the herein described beneficial results of a flow sensitivity by an outflow meter are still substantially retained.

One method of tempering is, for instance, produced by slightly trimming oil the corners of the valve 8 as indicated at 3l and at 32'. 'I'his allows passage 34 to be slightly exposed to passage 33, and passage 31 to be slightly exposed'to passage 38 during the position of valve 3 indicated in Figure 7, which corresponds to its position in Figure 2. High frequency flow uctuations past the valve I are thereby prevented during supercharging of the cabin by the damping action of the inlet venturi control.

It is to be understood that I do not limit myself to the particular forms or devices described in the preceding specification. Thus pressure sensitivity to effect a pressure control with my system might be derived from any equivalent pressure-sensitive device, as a flexible vapor pressure container having a volatile liquid therein at a constant temperature, for instance. Nor are the flow sensitive devices limited to venturis. Hot wire electrical ilow meters and various other species of flow meters are recognized equivalents,

to be exceeded, said diii'erential-pressure responsive means being automatically operable, so long as such differential tends to be exceeded, to maintain such diiferential of cabin pressure above external pressure, within the capacity of the pressure source.

3. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure to the cabin, and an outlet to discharge air from the cabin, two interconnected valve means operable the one to govern air movement through and the other to govand are properly adaptable to the control mechanisms described. By the use of the above mentioned volatile liquid as a basis of pressure control, or hot wire ilow meter as a ilow control, the type of pressure and flow regulations may be made to vary systematically with atmospheric temperature, or cabin temperature. Thus during usually high atmospheric temperatures at high altitudes which might, together with the temperature rise of air compression, cause uncomfortable cabin temperatures, the flow of air might be reduced to minimize the rate of heat contribution to the cabin and to reduce the cabin temperature. At the lower altitudes, however, the now may be advantageously increased during hot weather for maximum passenger comfort, because the heat of compression is relatively small at this time and the cabin temperature will be reduced by increased air flow within certain limits.

While I have referred to the passenger cabin as the space or enclosure within which the pressure is regulated, implying by that term the space, usually within the fuselage, occupied by passengers or crew, and while it is to such a cabin that the invention is primarily applicable the term is also to be understood as meaning any enclosed space ofan aircraft wherein, for any reason, it is necessary or desirable to maintain given pressure conditions.

What I claim as my invention is:

1. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure to the cabin, a pressure regulating means, absolute-pressure responsive means operatively connected to the pressureregulating means. and automatically operable thereupon to maintain cabin pressures substantially constant, up to a selected diiferential of cabin pressure above external pressure, and differential-pressure responsive means also operatively connected to the pressure-regulating means, and automatically operable thereupon to prevent exceeding such diierential for all lower external pressures.

2, Mechanism to control aircraft cabin pressures, comprising, in combination, meansto supply air under pressure within the cabin, valve means movable to regulate the cabin pressure, absolute-pressure responsive means operatively connected to the valve means, and automatically operable to maintain cabin pressures substantially constant, up to a selected differential of cabin pressure above external pressure, and differential-pressure responsive means also operatively connected to said valve means, and arranged to override automatically the absolute-pressure responsive means, during the prevalence of conditions tendlng to cause such selected diilerential ern pressure within the cabin, means operable primarily under the influence of cabin outflow pressure to operate said interconnected valve means to maintain a substantially constant cabin pressure, means operable automatically upon the attainment of a selected differential of cabin `pressure above external atmospheric pressure to operate said interconnected valve means to maintain such differential during the prevalence of lower external pressures tending to increase the differential.

4. Mechanism to control aircraft -cabin pressures, comprising, in combination with a supercharger connected to supply air to the cabin, and an outlet to discharge air from the cabin, a valve controlling inlet from the supercharger, a valve y controlling outflow from the cabin, means operable primarily under the influence of inlet flow pressure to differentially operate said valves to maintain a substantially constant rate of flow through the cabin throughout a given altitude range. means operable primarily as a function oi cabin outflow pressure to differentially operate said valves to maintain a substantially constant cabin pressure throughout a' higher altitude range, and means t0 selectively render operable one or the other oi said latter two means.

5. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected to supply air to the canin, and an outlet to discharge air from the cabin, a valve controlling inlet from the supercharger, a valve controlling outow from the cabin, means operable primarily under the inuence of inlet now pressure to differentially operate said valves to maintain a substantially constant rate of now through the cabin throughout a given altitude range, means operable primarily as a function of cabin outow pressure to diil'erentially operate said valves to maintain a substantially constant cabin pressure throughout a higher altitude range, means to selectively render operable one or the other of said latter two means. and means operable under the influence of an attained difierential oi' cabin pressure above external pressure to differentially operate said valves to malntain such differential throughout a still higher altitude range.

4. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected to supply air within the cabin, and an outlet to discharge air from the cabin, valve means operable to control such supply and discharge, means operable primarily as a function of inlet ilow pressure to control such valv means to maintain a constant rate oi' mf through the cabin throughout a low altitu e range, means responsive to a given pressure altitude to signal the attainment of the upper limit of such altitude range, means operable as a result of the operation ot the preceding means to alter the manner of control of the valve means, means thereafter operable primarily as a function of cabin outflow pressure to maintain a substantially constant cabin pressure throughout a medium altitude range, means operable in response to a given diierential ofcabin pressure over external pressure to override the preceding means and to control said valve means to substantially maintain such differential throughout a high altitude range, and signal means responsive to a given pressure altitude to indicate the attainment of a selected `minimum cabin pressure.

7. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected to supply air Within the cabin, and an outlet to discharge air from the cabin, an inlet valve and an outlet valve separately operable,I pressure sensitive means to effect movement of such inlet valve, a control valve operable, in one position, to subject said pressure sensitive means primarily to the influence of inlet flow pressure, thereby to move the inlet valve to effect a substantially constant rate of flow through the cabin, and operable, in another position, to subject said pressure sensitive means primarily to the influence of outlet flow pressure, thereby to move the inlet valve to tend to maintain constant pressure within the cabin.

8. Mechanism to control aircraft cabin pressures, comprising, in combination with a 'supercharger connected to supply air within the cabin, and an outlet to discharge air from the cabin, an inlet valve and an outlet valve separately operable, pressure sensitive means to effect movement oi such inlet valve, a control valve operable, in one position, to subject said pressure sensitive means primarily to the influence of inlet flow pressure, thereby to move the inlet valve to effect a substantially constant rate of ow through the cabin, and operable, in another position, to subject said pressure sensitive means primarily to the influence of outlet iiow pressure, thereby to move the inlet valve to tend to maintain constant pressure within the cabin, pressure sensitive means governing the operation oi said outlet valve, and an absolute pressure sensitive means connected and arranged to close said outlet valve with decrease of cabin pressure, thereby tending to maintain constant cabin pressure.

9. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected to supply air within the cabin, and an outlet to discharge air from the cabin, an inlet valve and an outlet valve separately operable, pressure sensitive means to eiTect movement of such inlet valve, a control valve operable, in one position, to subject said pressure sensitive means primarily to the influence of inlet dow pressure, thereby to move the inlet valve to effect a substantially constant rate of iow through the cabin, and operable, in another position, to subject said pressure sensitive means primarily to `the influence of outlet ow pressure, thereby to move the inlet valve to tend to maintain constant 'pressure within the cabin, pressure sensitive means governing the operation of said outlet valve, an absolute pressure sensitive means tending to close said outlet valve with decrease of cabin pressure, thereby tending to maintain constant cabin pressure, and a further pressure sensitive device operable asa function of pressure differences between cabin pressure and atmospheric pressure. operatively connected t0 override the' preceding absolute pressure sensitive means. and to eiiect movement oi' the outlet valve to maintain a substantially constant selected differential pressure within the cabin.

10. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within the cabin, and an outlet to dicharge air from the cabin, valve means controlling such inflow and outilow, an absolute pressure sensitive device operatively connected to control the valve means, and operable under the influence of a pressure drop within the cabin, through a selected critical range, to restrict the outilow, means operable primarily under the influence of outflow pressure to operate said valve means to maintain a nearly constant pressure, within the region of such critical range, and terminating at the lower limit thereof upon the attainment of a selected differential oi cabin pressure over external pressure, and differential pressure sensitive means operatively connected to control said valve means, to permit outflow and to maintain the selected differential pressure automatically at higher altitudes.

11. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within the cabin, and an outlet to discharge air from the cabin, an lnlet valve and an outlet valve arranged to be selfclosing upon failure of inflow pressure, and to be self-opening upon subjection to external pressure exceeding the cabin pressure, and means, including both an absolute-pressure sensitive means and a differential-pressure sensitive means, both operatively connected to said valves to control them to attain a cabin pressure exceeding the external pressure.

12. Mechanism to control aircraft cabin pres-- sures, comprising, in combination with a supercharger connected to supply air within the cabin, and an outlet to discharge air from the cabin, an inlet valve and an outlet valvearranged to be self-losing upon failure of indow pressure, and to be self-opening upon subjection to external pressure exceeding the cabin pressure, means operable primarily in accordance with outlet; flow pressure to control the inlet valve, whereby upon cessation of outflow the inlet valvewiil close automatically, and pressure sensitive means to control said outlet valve to attain and maintain cabin pressures in excess of the external pressures.

13. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected 'to Supply air Within the cabin,

and an outlet to discharge air from the cabin..

an inlet valve and an outlet `valve arranged to be self-closing upon failure of inilow pressure, and i to be self-opening upon 'subjection to external pressure exceeding the cabin pressure, means operable primarily in accordance with outlet now pressure to control the inlet valve, whereby" upon cessation of outiiow/the inlet valve will close automatically, and two pressure sensitive means operatively connected to control said outlet valve, one being sensitive to absolute pressures .to maln- .tain a substantially constant cabin pressure throughout a medium altitude range, and at the lower pressure limit of such range closing the outlet valve, and the other being sensitive to the dlierential of cabin pressure over external pressure then attained, to maintain such differential throughout a higher altitude range.'

14. MechanismV to control aircraft cabin pressures, comprising, in combination with an inlet to the cabin from a source of warm air under pressure, and an outlet to discharge air from the cabin, valve means controlling such inlet and outlet, and the inlet and the outlet being dis' posed one surrounding the other. for transference of heat to the outlet. in the vicinity of the valve means, to prevent ice formation.

15. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected to supply air to the cabin, and an outlet to discharge air Iromthe cabin, a venturi interposed between the supercharger and the cabin, an inlet valve between the supercharger" and said venturi, a second venturi between the cabin and the outlet, an outlet valve between the latter venturi and the outlet, means operatively connected to the inlet valve to move the same in accordance with a now pressure'through one or the other or said venturis, means selectively oper'- able to connect at will the inlet venturi or the outlet venturi lor control of said inlet valve, and pressure sensitive means to control said outlet valve.

16. Mechanism to control aircraft cabin pressures, comprising, in combination with a super charger connected to supply air to the cabin, and

' an outlet to discharge air from the cabin, a ilow sensitive device disposed in the supply connection and a second flow sensitive device disposed in the outlet, valve means controlling inflow and outiiow, .and means selectively operable to control said valve means under the inlluence of said iirst iiow sensitive means.`tending to maintain a constant rate of innow, or under the influence oi the second now sensitive means, tending to maintain a constant cabin pressure.

1 17. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected to supply air to the cabin, and an outlet to discharge air from the cabin, a now sensitive device disposed in the supply connection and a second ilow sensitive device disposed 'in the outlet, valve means controlling iniiow and outilow, means selectively operable to control said valve means under the iniluence ot said rst now sensitive means, tending to maintain a constant rate of inflow, or under the influence of the second flow sensitive means, tending to maintain a constant cabin pressure, and pressure sensitive means operable under the influence of an attained diilerential oi cabin pressure over atmospheric pressure, and further operable, upon the attainment of such diiierential, to control said valve means, tending to maintain such difierential.

18. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected to supply air to the cabin, and an outlet to discharge air from the cabin, a venturi interposed between the supercharger and the cabin, an inlet valve between the supercharger and said venturi, a second venturi between the cabin and the outlet, an outlet valve between the latter venturi and the outlet, a control piston and a servo piston operatively connected to the inlet valve, a control valve having two passages and -movable between two positions, its casing having two ports connected above and below the control piston, respectively, with which the passages connect in either position, andhaving tour additional ports, with two oi which the passages connect in one position, and connecting respectively to the inlet venturi flow pressure and to the supercharger static pressure, and with the other two of which the passages connect in the other position and connecting respectively to the outlet venturi flow pressure and to the interior of the cabin. whereby. in the nrst position the control piston and the inlet valve are operable under control oi iniiow to maintain a constant rate of now. and in the second position are operable under control oi' o`utiiow to tend to maintain a sures, comprising, in combination with a supercharger connected to supply air tol the cabin, and

an outlet to discharge air from the cabin, a venturi interposed between the supercharger and the cabin, an inlet valve between the supercharger and said venturi, a second venturi betweenthe cabin and the outlet, an outlet valve between the latter venturi and the outlet, .means operatively connected to the inlet valve to move the same in accordance with a flow pressure through one or the other of said venturis, means selectively operable to connect at will the inlet venturi or the outlet venturi for control oi said inlet valve, a pressure sensitive element and a servo piston operatively connected to control said outlet valve, a conduit leading supercharger static pressure to oneside o! said servo piston, tending to move it in a direction to open said outlet valve, a hollow stem movable with the valve and piston, and adapted to connect its opposite side to the atmosphere, whereby to control said valve as a function of the differential between atmospheric and supercharger pressures, the pressure sensitive element beingsubjected to cabin static pressure tending to collapse lt in a direction to permit opening of the valve, and a stem movable in response to movement or the pressure sensitive element, disposed to close the hollow stem-as the servo piston and valve move towards open position, and to eect closing oi' the valve as the pressure sensitive element expands, thereby tending to maintain a constant pressure within the cabin.

20. Mechanism to control aircraft cabin pressures, comprising. in combination with a supercharger connected to supply air to the cabin, and an outlet to discharge air from the cabin, a venturi interposed between the supercharger and the cabin, an inlet valve between the supercharger and said venturi, a second venturi between the cabin and the outlet, an outlet valve between the latter venturi and the outlet, means operatively connected to the inlet valve to move the same irraccordance with a flow pressure through one or the other of said venturis, means selectively operable to connect at will the inlet venturi or the outlet venturi for control of said inlet valve, a pressure sensitive element and a servo piston operatively connected to control said outlet valve, a conduit leading supercharger static pressure to one side of said servo piston, tending to move it in a direction to open said outlet valve, a hollow stem movable with the valve and piston, and adapted to connect its opposite side to the atmosphere, whereby to control said valve as a function of the difierentlal between atmospheric and supercharger pressures, the pressure sensitive element being subjected to cabin static pressure tending to collapse it in a direction to permit opening of the valve, a stem movable in response to movement of the pressure sensitive element, disposed to close the hollow stem as the servo piston Aand valve move towards open position. and to eii'ect closing of the valve as the pressure sensitive ele- `vent expands, thereby tending to maintain a mstant pressure within the cabin, a conduit Jnnecting to the atmosphere and leading to pie side of the servo piston opposite that which is subjected to the supercharger pressure, a normally closed valve in such conduit, and an element movable in accordance with an attained differential between cabin pressure and atmos'- pheric pressure to open the latter valve, thereby to subject the servo piston to a lowered atmospheric pressure and to move it, in opposition to the first pressure sensitive element, to open the outlet valve under the influence of such differential pressure, and to tend to maintain such differential.

2l. The method of controlling aircraft cabin pressures which comprises maintaining a substantially constant cabin pressure, by regulating inflow and outflow under the influence primarily of outflow pressure, through a selected medium altitude range, until a selected differential of cabin pressure over external pressure is attained, and then at higher altitudes maintaining such differential by regulating inflow and outflow under the influence of a `differential pressure sensitive device overriding the outflow pressure regulating device.

22. The method of regulating inflow' to and outflow from an air craft cabin which comprises maintaining a substantially constant rate'of inflow in accordance with inflow pressure, up to a selected altitude, from such altitude to a higher altitude maintaining a substantially constant attained pressure4 by regulating inflow and outflow primarily in accordance with outflow pressure. until a selected differential of cabin pressure over external pressure is attained, and at higher altitudes maintaining such differential primarily in accordance with such attained diierential.

23. In an aircraft, in combination, sustaining wings, a power plant and propellers to sustain flight at high altitudes, a cabin supported by the wings, the structure of said cabin including walls defining an airtight compartment, said walls being of desired but limited structural strength, an air supply conduit admitting to the interior of said compartment, and a port to discharge air therefrom, a pressure source to deliver air under pressure to the cabin through said air supply conduit, means to regulate the supply of pressure air from between said pressure source to the cabin, outlet valve means controlling discharge from the cabin, absolute pressure responsive means automatically operable to control said outlet valve to maintain cabin pressure substantially constant, up to a selected differential of cabin pressure above external pressure, at which differential the limit of strength of the cabin structure, within a selected safety factor, is approached, differentialpressure responsive means operable to control said outlet valve to maintain such differential, within the safety factor, for a lower external pressure, within the capacity of the pressure source, and means to adjust the supply-regulatlng means in accordance with the setting oLthe outlet valve, to balance supply with outflow, at the respective pressures,

24. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within and for discharge from the cabin, means to control the cabin pressure, differential-pressure responsive means always operable to regulate said control means, to prevent the cabin pressure exceeding a selected pressure above the external pressure, and means also operable to regulate said control means to-increase the cabin pressure to a value above the external, pressure, within the hunting differential fixed by said differential-pressure responsive means.

25. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within and for discharge from the cabin, means to control the cabin pressure, differential-pressure responsive means operable to regulate said contro1 means, to prevent the cabin pressure exceeding a selected pressure above the external pressure, and means automatically operable at a selected altitude to regulate said control means, and thereby to initiate increase of the cabin pressure to a value above the external pressure, within the limiting differential fixed by said differentialpressure responsive means.

26. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure to and for discharge from the cabin, means to control the cabin pressure, differential-pressure responsive means operable to prevent the cabin pressure exceeding a selected pressure differential above the external pressure, and means automatically operable at a predetermined altitude to regulate said control means, and thereby to initiate a change of cabin pressure relative to external pressure, at a predetermined rate as related to altitude, within the lower limit fixed by the external pressure and the upper limit xed by said differential-pressure responsive means.

27. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within the cabin, means to control the cabin pressure, differential-pressure responsive means automatically operable to regulate said control means to prevent cabin pressures from exceeding any selected diflerential above external pressure, and means automatically operable to regulate said control means, to maintain at all times a substantially constant rate of airflow through the cabin.

28. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure to the cabin, and an outlet to discharge air from the cabin, valve means operable to govern air movement through and pressure within the cabin, automatic control means to operate said valve means to maintaina substantially constant cabin pressure, a second automatic control means operable automatically upon the attainment of a selected diferential of cabin pressure above extenal atmospheric pressure to operate said valve means to maintain such differential during the prevalence of lower external pressures tending to lncrease the differential.

29. Mechanism to control aircraft cabin pressures, comprising in combination with means to supply air under pressure to the cabin, a discharge valvecontinually open for discharge of air from the cabin. differential-pressure responsive means operable to control said valve to prevent Aexceeding a given cabin pressure difierential over external pressures, and absolutepressure responsive means automatically operable, inside such dierentieL likewise to control said valve to maintain cabin pressures substantially constant.

30. Mechanism to control y aircraft cabin pres- Buns. comprising,

in combination with means to supply air under pressure to the cabin, means to regulate air-now through the cabin, absolutepressure responsive means operable to regulate said now-regulating means to maintain cabin external pressures, and means operable to regulate said now-regulating means to maintain at all times a substantially constant rate oi' air now through the cabin.

3l. The method of controlling aircraft cabin pressures which comprises regulating both the supply of air to and its discharge from the cabin, under the influence of the differential of cabin pressure over external pressure, to automatically prevent s uchdiiferential exceeding a selected value, and regulating both the supply of air to and its discharge from the cabin to attain a selected cabin pressure which is not in excess of the selected diiferential value.

32. Mechanism for controlling the pressure within an aircraft cabin, comprising a valve for controlling the iiow of air through such cabin, operating means for said valve, said operating means communicating with external atmospheric pressure, and means operable to regulate such temal atmospheric pressure, and means responsive to cabin interior pressure operable to regulate such communication of said operating means with the external atmospheric pressure, thereby 34. Mechanism to control aircraft cabin pressures comprising, in combination, means to supply air under pressure tothe cabin, an outlet from the cabin normally open for continuous outflow at all altitudes, means controlling the airilow through the cabin to prevent the cabin pressure from exceeding a selected pressure above external pressure, and means to increase the cabin pressure to a value above the external pressure but not greater thanl the limiting differential determined by said second-named means.

35. Mechanism to control aircraft cabin pres-- sures comprising, in combination with an outflowl opening and with means to deliver air under pressure within the cabin at a rate in excess of that necessary to maintain a given pressure within the cabin, dow-control means, absolute-pressure responsive means automatically operable to regulate said flow-control means to increase cabin pressures to values above external pressure, up

toa selected' differential of cabin'pressure aboveI external pressure, While at thesame time permitting continuous outflow through the outflow opening,` and dierential-pressure responsive means also operable to regulate said flow-control means to prevent exceeding such di'erential for all lower external pressures.

36. Mechanism for controlling the pressure within an aircraft cabinV comprising means for supplying all' under pressure within the cabin, an outlet valve, control means for said valve'operable to produce a cabin pressure in excess of external pressure, and a second control means for said to govern the cabin pressure. y

valve operable to prevent the attainment of a cabin pressure in excess of a selected diii'erential over external pressure.

37. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within the cabin, means movable to regulate flow through and pressure within the cabin, diiferentidl-pressure responsive means operatively connected to the regulating means, and automatically operable thereupon to prevent the cabin pressure exceeding a selected differential, and absolute-pressure responsive means also operatively connected to the same regulating means, and automatically operable thereupon to eiiect elevation of cabin pressure above external pressure.

38. 'Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within the cabin, means movable to regulate pressure within the cabin, diiIerential-pressure responsive means operatively Vconnected to the regulating means, and automatically operable thereupon to prevent the cabin pressure exceeding a selected diiierential.

absolute-pressure responsive means also operatively connected to the same regulating means, and automatically operable thereupon to eii'ect elevation of cabin pressure above external pressure, and now-control means regulating the rate of pressure air supply, to maintain balance thereof with the pressure-controlling means at mini-l mum rates of iiow.

39. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within the cabin, an outow valve movable to regulate pressure within the cabin, differential-pressure responsive means operatively connected to said outow valve, and automatically operable thereupon to prevent cabin pressure exceeding a selected diierential, and absolute-pressure responsive means also operatively connected to said outilow valve, and automatically operable thereupon to eect elevation of cabin pressure above external pressure.

40, Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within the cabin, an outflow valve movable to regulate pressure within the cabin, differential-pressure responsive means operatively connected to said outow valve, and automatically operable thereupon to prevent cabin pressure exceeding a selected differential,A

, and an outlet to discharge air from the cabin, an

inlet valve and an outlet valve separately operable, an absolute-pressure sensitive means tendmg to nose said outlet valve hun decrease or cabin pressure, thereby tending to retain a cabin pressure elevated above external pressure, a further pressure sensitive device operable as a function of pressure differences between cabin pressure and atmospheric pressure, operatively connected to override said absolute-pressure sensitive means, and thereby to prevent the cabin pglessure exceeding a selected diiferential, and

means operable primarily under the iniluence of rate of flow, to regulate saidinletvalve to maintain the pressure elevated within the cabin, and within the control capacity of the outlet valve and its controls. a

42. Mechanism to control aircraft cabin pressures, comprising, in combination with a connection for supply of air under pressure to the cabin, and a connection for discharge of air from the cabin. a valve controlling flow-through, and therefore the cabin pressure, pressure-sensitive means to adjust said valve for control of cabin pressure, including a venturi in one such connection. and servo means operatively connected to said venturi to eii'ect movement oi the valve under control oi the pressure-sensitive means.

43. Mechanism to control aircraft cabin pressures, comprising, in combination with a supercharger connected to supply air to the cabin, and an outlet to discharge air from the cabin, a venturi between the cabin and the outlet, an outlet valve controlling outilow from the cabin. pressure-sensitive means operatively connected to adjust said outlet valve for control of cabin pressure, and servo means operatively connected to said pressure-sensitive means to eil'ect movement of the valve under control of the pressuresensitive means.

44. The method oi' regulating aircraft cabin pressures which comprises supplying air under pressure within the cabin, while permitting continual outflow therefrom, regulating such outflow under the influence of the differential of cabin pressure over external pressure, in such manner that a selected differential can never be exceeded, and also restricting such outflow under the inuence ci cabin absolute pressure, in such manner as to build up cabin pressure to a value exceeding external pressure, up to the selected limiting differential.

45. The method of regulating aircraft cabin pressures which comprises supplying air under pressure within the cabin, while permitting continual outiiow therefrom, regulating such outflow under the iniiuence oi.' the ditlerential of cabin pressure over external pressure, in such manner that a. selected diderential can never be exceeded, and also restricting such outiiow under the inuence of cabin absolute pressure, in such manner as to build up cabin pressure to a value exceeding external pressure, up to a selected limiting diierential, meanwhile balancing inflow in accordance with a ilow factor. tosupply adequate pressure for diierential-pressure and absolute-pressure control, without excessive pressure or rate ot inow.

46. The method of regulating aircraft cabin pressures, which comprises supplying air under pressure within the cabin, while permitting continual outflow therefrom, maintaining a substantially constant rate oi' inflow in accordance with inow pressure. up to a selected medium altitude, from such altitude upwardly, through a medium altitude range, restricting outiiow under the iniiuence oi' cabin absolute pressure to build up cabin pressure to a value exceeding external pressure, and at high altitudes regulating outflow under the influence of the differential ci cabin pressure over external pressure, in such manner that a selected differential can never be exceeded.

47. The method o! regulating aircraft cabin pressures. which comprises supplying air under pressure within the cabin, while permitting continual outiiow therefrom, maintaining a substantially constant rate o! inflow inaccorciance` with inflow pressure, up to a selected medium altitude. from such altitude upwardly, through a medium altitude range. restricting outfioiv under the influence of cabin absolute pressure to build up cabin pressure to a value exceeding external pressure, and at high altitudes regulating outow under the iniluence or the differential of cabin pressure over external pressure, in such manner that a selected differential can never be exceeded, and, throughout the medium and high altitude ranges, regulating inilow in accordance with rate oi outflow, to supply adequate pressure for absolute-pressure and diiierentiul-pressure control, but to prevent the iniiow o1' under pressure at a rate materially in excess ci that required by the same.

48. Mechanism for controlling pressure Within an aircraft cabin comprising means for continuously supplying air under pressure tc such cabin and for discharging it therefrom. mean." to increase the cabin pressure to a value above the external pressure, and means autoinatlcalir operable to modify the action of said pressure increasing means, to prevent the cabin pressure exceeding a selected pressure above external pressure.

49. Means to regulate aircraft cabin pressure, comprising an outflowT valve biased te close means operable under the influence ci cabin pres-xsure, and operatively connected to the valve hold it open, at all altitudes, for outow, but only sumciently, at certain altitudes, to create an elevated cabin pressure, and a control, operable in accordance with the difference oi cabin pressure over external pressure, and operatively connected to said valve to automatically prevent such differential exceeding a selected value.

50. Means to regulate aircraft cabin pressure, comprising an outflow valve biased to close, servo means operatively connected to the valve, and subject to a diierence of the pressure to which the cabin is subjected, over external pressure, said servo means being organized and arranged to maintain the valve open so long as cabin pressure equals or exceeds external pressure, and differential-pressure responsive means operatively connected to the valve to open the latter increasingly in accordance with a tendency to increase the diiierential pressure, thereby to prevent such differential exceeding a selected value.

5l. Means to regulate aircraft cabin pressure,

comprising an outilow valve, biased to close, servo means operatively connected to the valve, control means operatively associated with said servo means, and subject to a diierence of cabin pressure over external pressure, said servo means and said control means being organized and arranged to open the valve increasingly with increasing diiferential pressure, thereby to preventY such differential exceeding a selected value.

52. Means to regulate aircraft cabin pressure,

comprising an outilow valve biased to close, servo means operatively connected to the valve, control means operatively assoclated with said servo means. and subject to a diterence oi' cabin pressure over external pressure, said servo said control means being organized and arrsnsd to open the valve increasingly with incre g differential pressure, thereby to prevent such differential exceeding a selected value, and a second control means operatively associated with said servo means. arranged for automatic operation alternatively with said diiTerential-pressure sensitivemeans, and itself subject to cabin absolute means pressure, said servo means and said second control means being organized and arranged to close the valve increasingly with increasing altitude, thereby to maintain cabin pressure elevated above external pressure, within the limiting differential iixed by said-differential-pressure sensitive means.

53. Means to regulate aircraft cabin pressure. comprising an outilow valve biased to seat, a piston operatively connected to move the valve, conduit means to subject the piston to a higher and l a lower pressure, upon its opposite sides, tendduit means to subject the piston to a higher anda lower pressure, upon its opposite sides, tending to unseat the valve, a control means to resillate the pressure difference acting upon said piston, and thereby the position or said val've and the cabin pressure. said control means being sensitive to the differential of cabin pressure over external pressure, and being organized and arranged. relative to said piston and valve. to prevent cabin pressure exceeding a selected differential, and a second control means arranged for automatic operation under the influence of cabin absolute pressure, alternatively with the diierential-pressure sensitive control, and itself operable, at cabin pressures within the limiting diilerential, to subject the piston upon opposite sides to a higher and a lower pressure, respectively, whereby the valve is held open by a force which is primarily dependent upon cabin absolute pressure, and the cabin pressure is automatically maintained at a value above external pressure.

55. Means to regulate aircraft cabin pressure, comprising an outflow valve and a seat therefor. a servo piston operatively connected toV said valve, and biased to close the valve, but subject to cabin pressure on one side, tending to open the valve, means to subject the piston, on its opposite side, to external pressure, likewise tending to open the valve with increase of altitude, and means adinstable in accordance with change of cabin pressure to maintain equilibrium between the valveopening forces active upon said piston and the biasing forces tending to close the valve, to permit closing of the valve with increasing altitude, and thereby tending to maintain cabin pressure at an elevated value with increase of altitude. l 56. ,Means to regulate aircraft cabin pressures, lunder the iniluence of an air pressure supply, comprising an outflow valve movable towards closed position to conserve cabin pressure and openable to decrease the same, a servo piston opperatively connected to said valve, and biased to closethe valve,y but subject to cabin. pressure on one side, tending tol open the valve. means to apply lower external pressures'to the opposite side of the piston. also tending to open the valve, the several forces thus acting upon the piston "1 being arranged in equilibrium to maintain a given cabin pressure corresponding to each altitude, and means sensitive to change of altitude reacting to alter the last-mentioned meanaand there- Ill) by to destroy the equilibrium of forces, to permit closing of the valve with increasing altitude, and thereby tending to maintain cabin pressure at an elevated value with increase of altitude.

67. Means ,to regulate the pressure within an aircraft cabin, which is elevated under the mnuence oi an air pressure supply, said regulating means comprising an outflow valve closable to conserve cabin pressure and openable to decrease the same, absolute-pressure sensitive means operatively connected to said valve, and automatically operable in accordance with increase of altitude above a given value, to move said valve progressively towards closed position, with such increase of altitude, tending to maintain a constant cabin pressure, and means operatively connected to said valve, and automatically operable to open the valve in accordance with the differential of cabin pressure over external pressure,`

above a given value, to prevent such diilerential being exceeded.

58. Means to regulate aircraft cabin pressures. under the innuence of an air pressure supply, comprising an outflow valve, closable to conserve cabin pressure and openable to decrease the same, means operatively connected to said valve. and automatically operable to move the valve towards open position in accordance with the differential of cabin pressure over external pressure, to prevent the cabin pressure exceeding a selected differential under all circumstances, and means also operatively connected to said valve. and automatically operable to move the valve towards closed position in accordance with increase of altitude above a given value, to prevent drop of cabin pressure at as rapid a rate as the external pressure drops, with increase of altitude.

59. Means to regulate aircraft cabin pressures, under theiniiuence of an air pressure supply, comprising an outilow valve closable to conserve cabin pressure and openable to decrease the same. means operatively connected to said valve, and automatically operable to move the valve towards open position in accordance with the differential of cabin pressure over external pressure, to prevent the cabin pressure exceeding a selected differential under all circumstances, and means also operatively connected to said valve. and automatically operable to move the valve towards closed position in accordance with increase of altitude above a given value, to progressively increase the difference of cabin pressure over` external pressure, with increase of altitude, and within the limiting differential fixed by said differential-pressure sensitive means, Y

80. An aircraft'cabinprgssure control comprising an outflow valve, a piston directly connected to said valve to movethe latter, the piston-valve assembly being biased to close, passages to subject the piston on one side to cabin pressure and on the other side to a lower pressure, tending to hold the outflow valve open, control means arranged to regulate ilow through the low-pressure passage,

and thereby the pressure difference at opposite 'sidesof the piston and the position of equilibrium of the outflow valve, and pressure-sensitive means, cooperating with said control valve meansrand arranged for movement in res use to change of cabin pressure, to automat cally shift said control valve means, and thereby to compensatingly adjust the outilow valve.

6l. In a cabin pressure control, an outflow valve. a Dlstonconnected to saidvalve to move the latter, the piston-valve assembly being biased' to close, passagesY to subject the piston on one side to cabin pressure and on the other side to a lower pressure, tending to hold the valve open. control valve means arranged to regulate the pressure diil'erence at opposite sides of the piston, said control valve means including a hollow stem included in the passage which admits to one side of the piston, and an aligned valve stem movable with the outow valve, and normally materially restricting ilow through the hollow stem, and a pressure-sensitive means arranged for movement in response to change in the difference of cabin pressure over external pressure, and operatively connected to shift said hollow stem relative to the cooperating valve stem, and thereby to compensatingly adjust the outilow valve.

62. The control as defined in claim 61, wherein the pressure-sensitive means is an absolutepressure sensitive means, exposed to and responsive to changes in cabin pressure.

63. The control as dened in claim 6l, wherein the pressure-sensitive means is a diilerentialpressure sensitive means, exposed to and responsive to changes in either of the external pressure and the cabin pressure.

64. A system for the control of pressure within an aircraft cabin, comprising a source of air under pressure connected to discharge within the cabin, means variably controlling outilow from the cabin, conformably to external atmospheric pressure at different altitudes, to create a difference oi cabin pressure over external pressure, and means to vary the rate of delivery from the pressure source to the cabin, conformably tothe outflow rate and desired pressure difference, to maintain such pressure diiierence without excessive rate of ow.

65. A system i'or the control of pressure within an aircraft cabin, comprising a source of air` under pressure connected to discharge within the cabin, valve means controlling outflow. means sensitive to external atmospheric pressure arranged to variably regulate said valve means in conformity to external pressure at diii'erent altitudes, tocreate an elevated cabin pressure, and means sensitive to iiowA through the cabin to vary the rate of delivery to the cabin from the pressure source, coniormably to the rate of discharge past the valve means, to maintain such elevated cabin pressure, and continual ventilation, without an excessive rate of iiow.

66. A system for the control of pressure within an aircraft cabin, comprising a blower connected to discharge within the cabin, a valve and pressure-sensitive control means therefor automatically controlling outow from the cabin to create cabin pressures which, above a selected altitude, l

are elevated above external pressures, and means sensitive to flow through the cabin to regulate the rate of delivery from the blower to the cabin, conformably to the ratei of discharge past the valve means.

67. A system for the control of pressure athin an aircraft cabin, comprising a source of under pressure connected to discharge within the cabin, means to "regulate the eilective rate of pressure supply to the cabin, means variabiy controlling outnow from the cabin, conformably to external atmospheric pressures at dierent altitudes. to create a difference of cabin`pressure over external pressure. and means sensitive to reduction ,of outnow, and automatically operable thereby to adjust said pressure-supply-regulating means to increase the effective rate of pressure supply. and vice versa, thereby to maintain ferentiaL the desired pressure difference, without excessive rate of ilow.

68. Mechanism to control aircraft cabin pressures, comprising in combination with means to supply air under pressure to the cabin, an outflow valve continually open for discharge of air from the cabin, differential-pressure responsive means operable to control said valve to prevent exceeding a given cabin pressure differential over external pressures, and absolute-pressure responsive means automatically operable, likewise to control said valve, to create a cabin pressure which is elevated above external pressure.

69. Mechanism to control aircraft cabin pressures, comprising in combination with means to supply air under presure to the cabin, means to allord and control continual ilow through the cabin, differential-pressure responsive means operable to control said flow-controlling means to prevent exceeding a given cabin pressure differential over external pressures. and absolutepressure responsive mea'ns automatically operable. inside such differential, likewise to control such now-controlling means, to create a cabin pressure which is elevated above external pressure. l

70. Mechanism to control aircraft cabin pressures, comprising, in combination with means to supply air under pressure within the cabin, means operable to regulate pressure within the cabin, diiferential-pressure responsive means operatively connected to said pressure-regulating means, and automatically operable thereupon to prevent cabin pressure exceeding a selected difand absolute-pressure responsive means also operatively connected to said pressure-regulating means, and automatically oper-v able thereupon to eiect elevation of cabin pressure above external pressure and means to regulate the supply of pressure air in conformity i with pressure conditions as determined by said pressure-regulating means, and within the capacityof the latter and its controls.

71. Mechanism for control of aircraft cabin pressures, comprising, in combination with means to supply air under pressure within theA cabin, and an outow port continually open at all altitudes. dierential-pressure responsive means to regulate outnow through said port, to prevent cabin presure exceeding a selected diil'erential over external pressure, and absolute-pressure responsive means also regulating such outiiow through said port, to create an elevated cabin pressure.

72. Means to regulate pressure within an aircraft cabin, comprising valve means closable to restrict outflow relative to inflow and thereby to increase cabin pressure. and means sensitive to external pressure operatively connected to close or open said valve means at a rate which is a function oi' the rate of change of such external pressure, and thereby to vary the cabin pressure at a rate bearing a predetermined relation to the rate of changent external pressure, and differential-pressure sensitive means operatively connected to modify the action of said valve means. to prevent cabin pressure from exceeding the external pressure by more than a selected amount. l

73. A system for the control of pressure within an aircraft cabin which has an inlet port and an outlet port continually open for ventilating flowthrough, comprising means controlling airiiow through one port, and separate means controlling airiiow through the other port, now-sensitive means governing one such airflow-controlling means. to limit the rate of flow-through, and pressure-sensitive means governing the other such airflow-controlling means, to increase cabin pressure over external pressure.

74. A system as in claim 73, characterized in that the flow-sensitive means governs inflow, and the pressure-sensitive means governs outflow.

'75. A system as in claim 73, characterized in that each of the airflow-controlling means is a valve, varlably open to govern flow-through or cabin pressure, as' the case may be.

76. Mechanism for controlling the pressure within an aircraft cabin comprising means to supply air under pressure within the cabin, an outlet valve, vand twocontrol means for said valve, -one oi' said control meansbeing sensitive to absolutel pressure, and being operatively connected to said valve to maintain cabin pressure elevated above external pressure during a given altitude range, and the other of said control means being sensitive to the difierenceof cabin pressure over external pressure, and being operatively connected to said valve to maintain a selected did'erential through a different altitude range.

77. Mechanism` for controlling the pressure within an aircraft cabin comprising means to supply air under pressure within the cabin, valve means to regulate outiiow and hence pressure within the cabin, a control device sensitive to absolute pressure, and a second control device` sensitive to the difference of cabin pressure over external pressure, each of said control devices being operatively connected to the valve means to maintain cabin pressure elevated above external pressure through a selected altitude range, and to maintain a cabin pressure differential which is not in excess of a selected value for a. different selected altitude range.`

78. Mechanism for controlling the pressure within an aircraft cabin comprising means to supply air under pressure within the cabin, an outflow valve. two control means operatively connected to the valve, one of said control means being operable automatically in accordance with the relation of cabin pressure to external pressure, to prevent a selected relationship being 1 exceeded, at any altitude, and the second being sensitive `to a cabin pressure factor, to automatically create and maintain cabin pressure elevated above exterior pressure, from a selected altitude upward, within the limit fixed by said first-mentioned control.

"19. Mechanism for controlling the ressure within an aircraft cabin whereinto fre air is supplied under pressure and whence stale air is discharged, comprising a device to regulate inflow and a device to regulate outflow, said devices cooperatively constituting a means to regulate pressure within the cabin, a flow-sensitive control operatively connected tosaid pressuref 'regulating means to maintain a predetermined rate of now through the cabin, regardless of cabin pressure or of external pressure, and a pressure-sensitive control operatively connected to `said pressure regulating means to create a predetermined elevated cabin pressure through out a selected altitude range.

80. Mechanism as set forth in claim 79, characterized in that the inflow andoutfiow regulatr ing devices are operative at all altitudes to create a continuous ow through the cabin,A and the now-sensitive device is also operative at all altitudes to maintain a substantially constant rate of flow through the cabin.

8l. Mechanism as set forth in claim '79, characterized in that the pressure-sensitive control includes th an absolute-pressure control to create elevated cabin pressures throughout at least a portion of the selected altitude range, and a diiferentialpressure control to limit the differential pressure throughout some portion of such selected altitude range.

82. Mechanism for controlling the pressiue within an aircraft cabin whereinto fresh air is continuously supplied under pressure and whence stale air is continuously discharged. at all altitudes, comprising a device to regulate inflow and a ,valve continuously open at all altitudes to regulate outflow, said device and said valve cooperatively constituting a means to regulate pressure within the cabin, an absolute-pressure control and a diiIerential-pressure control each operatively connected to said pressure-regulating means to maintain a substantially constant rate of flow through the cabin, regardless of cabin pressure, and to create a cabin pressure which is elevated above external pressure throughout a selected altitude range, and to limit the differential of cabin pressure over external pressure throughout a portion, at least, of such selected altitude range.

83. Mechanism to control the pressure within an aircraft cabin, whereinto airis supplied under pressure, comprising an outow valve, pressuresensitive means. conduit means connecting said pressure-sensitive means to a high pressure source which is related to the cabin pressure, and to atmosphere and said pressure-sensitive means being operatively connected to move said valve, and means to vary the rate of ow through one oi said conduit means, and relative to the rate of now through the other, thereby to vary the pressure diiierence acting upon said pressuresensitive means, and hence thefsetting of said outflow valve.

84. Mechanism to control the pressure within an aircraft cabin, whereinto air is supplied under pressure, comprising valve means to control now through and hence pressure within the cabin, pressure-sensitive means operatively connected to move said valve means, conduit means connecting said pressure-sensitive means to a high pressure source related `to the cabin pressure and to atmosphere means, to vary the relative rate of flow through said conduit means, thereby to vary the pressure diiference acting upon said pressure-sensitive means, and hence the setting ofsaid valve means.

85. Mechanism nto control the pressure within an aircraft cabin, whereinto air is supplied under pressure, comprising valve means to control flow through and hence pressure within/the cabin, pressure-sensitive means operatively connected to move saidfvalve means, conduit means connecting said pressure-sensitive means to a cabin inlet pressure source and to an atmospheric pressure source, and means to vary the. relative Arate of flow through said conduit means, thereby to vary the pressure diderence acting upon said pressure-sensitive means, and hence the setting of said valve means, said mechanism further including means to govern said rate-of-flowvarying means automatically in accordance with a cabin pressure factor. n

86. Mechanism to control the pressure within an aircraft cabin, whereinto air is supplied under pressure, comprising an outow valve. pres- 

